1. Field of the Invention
The present invention relates to a thermoelectric device comprising a thermoelectric element composed of principally thermoelectric material.
2. Description of the Prior Art
A thermoelectric device comprising a thermoelectric element principally composed of thermoelectric material is well known. The known thermoelectric device has two types of usages, one is as a cooling-heating type device which can cool or heat when electricity is supplied, and the other is as a power generation type which can generate electricity when being cooled or heated.
A known conventional thermoelectric device is disclosed in pages 24 to 25 of xe2x80x9cThermoelectric Transfer System Technical General Handbookxe2x80x9d published by Realize Company on Jun. 30, 1995 (heisei 7). The nickel plating layer of this device prevents the solder ingredient of the solder layer from spreading into the thermoelectric element, and consists of a single layer. Therefore, the conventional thermoelectric device has advantages of long life and reduced degradation in use.
Furthermore, in general, the thermoelectric element composed of thermoelectric material is hard to solder. The nickel plating layer prevents the solder ingredient of the solder layer from spreading into the thermoelectric element, and degrades the soldering characteristic of the thermoelectric element when the thermoelectric element is assembled.
Increased restraint of the spread of the solder ingredient together with improved soldering are desired in the industry. However, a single layer nickel plating is inadequate for combining the characteristics of improved spread prevention and improved soldering. In other words, if the nickel plating layer is designed for a high level of spread prevention, it can prevent the solder ingredient of the solder layer from spreading the inside of the thermoelectric element, but then it has an insufficient solder wetting property. On the other hand, if the nickel plating layer is designed for a high solder wetting property, it is sufficient for spread prevention.
An object of the present invention is to solve the above-mentioned disadvantages, and more specifically, to provide a thermoelectric device having both a high soldering property and high spread prevention.
According to a feature of the present invention, the above and other objects are addressed by a thermoelectric device comprising a thermoelectric element composed of principally thermoelectric material, a counter element adhered to said thermoelectric material, a solder layer lying between said thermoelectric element and said counter element and adhering said thermoelectric element to said counter element, and a restraining layer located between said thermoelectric element and said solder layer, wherein said restraining layer comprises a first layer having a composition to prevent said solder ingredient of said solder layer from spreading into said thermoelectric element, and a second layer composed of material having a higher wetting property than said first layer with respect to said solder layer.